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Reference design uses 2-channel battery sensor interface with 8-bit microcontroller

Mon, 07/30/2012 - 4:20pm

ams announced a reference design which shows how a simple current and voltage measurement circuit can produce state-of-charge (SOC) readings for electric scooter batteries.
The reference design uses the AS8510 sensor interface from ams, a two-channel battery sensor interface, together with a simple 8-bit microcontroller, an LDO and an LED driver (driving an LED bar-graph display). The bill-of-materials cost for these active components is around $3.70.

By implementing this design, electric scooter manufacturers can replace today’s crude voltmeter displays with a fuel gauge, thus making the vehicle more useful and convenient to the rider while adding little to its bill of materials.

Electric scooters are normally powered by four series-connected 12-volt lead-acid batteries and are an increasingly popular mode of transportation because they are cheap to buy and run, and emit no exhaust fumes. But the voltmeter dials provided in them offer a poor indication of the scooter’s range, since the output voltage at the batteries has a non-linear relationship with SOC, and varies markedly depending on the load on the batteries.

The new e-scooter fuel-gauging reference design from ams succeeds in meeting the tight cost requirements of electric scooter manufacturers while delivering accurate voltage and current readings across the charge/discharge cycle and across the battery’s operating temperature range. This is due in large part to the circuit’s use of the AS8510 sensor interface, which integrates data acquisition and data conversion in a single chip, and which produces virtually offset-free current and voltage measurements across a wide dynamic range.

The ams circuit design captures simultaneous current and voltage measurements for each of the four batteries at a high sampling rate. Demonstration software implemented in an 8-bit microcontroller converts a combination of open-circuit voltage measurements and coulomb counts into SOC readings. The reference design supports a simple LED bar graph display, but it can also be used to drive a more expensive LCD display, providing more precise SOC information to the rider. The software developed by ams is provided at no cost to demonstrate that fuel gauging can be successfully implemented in the reference design hardware, and to show how accurate voltage and current measurements can be used to produce valid SOC readings.

 
ams
www.ams.com.

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